The present invention concerns, in accordance with a first aspect, a method of seeking images, using an example image, from amongst a plurality of images stored in a database, each of the stored images being associated with a data item representing at least one characteristic of the visual content of the image. The invention also concerns a device able to implement such a method.
According to a second aspect, the present invention concerns a method of indexing digital images taking into account the location of regions of interest in the images. The invention also concerns a method of seeking images from an example image, from amongst a plurality of images stored in a database, the images being indexed according to the above-mentioned indexing method. The invention also concerns a device able to implement such methods of indexing and seeking images.
A conventional method of seeking digital images in a database containing images is based on a system of indexing the images in the database.
The purpose of the indexing system is to associate, with each image in the base, an item of information characteristic of the content of the image referred to as the index of the image. All these information items form the index of the database.
A user can then interrogate the image database through a request containing an item of information characteristic of the type of image sought. The content of the request is then compared in accordance with a search strategy with the content of the index of the database.
Finally, the image in the base whose indexed information item has the greatest similarity to the content of the request is then extracted. A plurality of images extracted from the base can also be presented to the user, ordered according to their degree of similarity to the request.
In a traditional system of indexing digital images, the index of the database is composed of textual descriptors of the images stored.
The request of the user then consists of key words describing the characteristics of the content of the image to be sought.
This type of indexing by textual descriptors has the drawback of being imprecise, in particular because the same image may be described in different ways by different users.
In order to mitigate this type of drawback, the need has therefore been felt to develop techniques for representing and extracting the semantic content of a digital image.
Methods have appeared in which an image is characterised according to the distribution of the colours or textures making it up.
In other methods, an image is characterised by the shape or contour of an object making it up.
However, all these descriptors, referred to as xe2x80x9cprimitivesxe2x80x9d, of the image, reflect only physical characteristics of the image, and are therefore of a low semantic level.
In order to increase the semantic character of the indexing of the images, indexing systems which use a combination of low-level primitives are beginning to appear.
One of the most well-known is certainly the QBIC (xe2x80x9cquery-by-image-contentxe2x80x9d) system developed by IBM.
To obtain more details on this system, reference can be made to the article xe2x80x9cThe QBIC Project; Querying Images by Content Using Color, Texture, and Shapexe2x80x9d, by Niblack, W et al., which appeared in IBM Computer Sciences Research Report, pp 1-20 (Feb. 1, 1993). Reference can also be made to U.S. Pat. No. 5,579,471 of IBM entitled xe2x80x9cImage query system and methodxe2x80x9d. 
The QBIC system makes it possible to find digital fixed (or video) images from a request by means of the example. In the particular case of fixed images, this request is defined either as a complete image or as an object with a rectangular or arbitrary shape, extracted from an image or defined by the user.
The content of the images in the database is characterised by its colour distribution (histogram), texture and shape.
Where the request is defined as a portion, also referred to as a region, of an image, the similarity measurement also takes account of the spatial position of this region.
However, in the QBIC system and in the indexing systems of this type, the indexing of an image stored in the database relates to the entire content of the image, without consideration of the zone or region which particularly represents the visual content of the image.
Moreover, the request at best relates only to a single portion of the example image.
However, in a given image, several distinct regions may contain a great deal of semantic information. Consequently, in spite of the combination of several primitives for indexing the content of the image, this type of index is not sufficiently representative of the semantic content of the image.
Thus, in the indexing systems of the QBIC system type, an analysis of the similarity between an index derived from a request and that derived from a stored image is normally still insufficiently precise.
In the following description, the expression xe2x80x9cregion of interestxe2x80x9d (ROI) is used to mean a delimited portion of a given image predefined as containing elements characteristic of the visual content of the image, that is to say as containing a great deal of semantic information.
The present invention aims to remedy the aforementioned drawbacks of the search and indexing systems of the prior art.
To this end, in accordance with a first aspect, the present invention concerns a method of seeking images, from an example image, from amongst a plurality of images stored in a database, each of the stored images being associated with a data item of a first type representing at least one characteristic of the visual content of the image. In accordance with the invention this image search method includes the following steps:
each time a new image is stored in the database, associating with the new image a data item of a second type representing the location of at least one region of interest in the new image;
receiving a data item of the second type representing the location of at least one region of interest in the example image;
obtaining a data item of the first type associated with the example image;
calculating a similarity between the example image and each of the images amongst at least one subset of said stored images, the similarity being calculated from the data of the first type and of the second type associated respectively with the example image and with the stored image; and
supplying at least one image, referred to as the result image, of the database, the result image being selected from amongst the stored images in the database according to its degree of similarity with the example image.
In this way, taking account of the data representing the location of at least one region of interest (data item of the second type), in the example image and in the images of the database, the search for images in the database is more precise. This is because on the one hand, for each image in the database, the database manager has taken care to isolate the semantic content of the image through this data item of the second type. The user, on the other hand, through the data item of the second type associated with the example image, can also specify his request by choosing in the image certain regions which correspond to the one which he wishes to find. Consequently there is obtained a similarity closer to reality compared with the one obtained when this type of data is not taken into account both in the example image and in the images in the database.
The present invention also concerns a device for seeking images, from an example image, from amongst a plurality of images stored in a database. In accordance with the invention this device has means adapted to implement an image search method as succinctly defined above.
The present invention also concerns a computer, comprising such an image search device or means adapted to implement the above-defined image search method. The invention also relates to a computer program including one or more sequences of instructions able to implement the above-defined image search method when the program is loaded and executed in a computer. The invention also relates to an information carrier, such as a diskette or compact disc (CD), characterised in that it contains such a computer program.
The advantages of this device, computer, computer program and information carrier are identical to those of the method as succinctly disclosed above.
In accordance with a second aspect, the present invention concerns a method of indexing a digital image. According to the invention, this indexing method comprises the following steps, for each image Im, to be indexed;
dividing the image plane of the image Im, in accordance with a partitioning including a predefined number N of blocks Bi;
extracting from each of the blocks a data item of a first type representing at least one characteristic of the visual content of the block;
defining in the image at least one region of interest, and obtaining a data item of a second type representing the location of at least one region of interest in the image;
calculating for each of the blocks Bi a first coefficient, WiIm, indicating a degree of presence in the block under consideration of the image of the region or regions or interest;
associating with the image Im an index composed of a first vector G(Im), having N components, each of which being one of the data items of the first type, and a second vector W(Im), having N components, each of which being one of the first coefficients WiIm.
In this way, there is obtained for each image an index which is much more precise with regard to its representativeness with respect to the semantic content of the image. This is because the index thus obtained takes into account the data item representing the location of at least one region of interest (data item of the second type) by means of the vector W(Im) and the data item representing at least one characteristic of the visual content of the image per block of the image (data item of the first type) by virtue of the vector G(Im). Combining these two types of data by blocks issuing from a division of the image also helps to increase the precision of the index associated with the image.
Correlatively, the invention concerns a method of seeking images, from an example image, from amongst a plurality of images stored in a database. This image search method is characterised by the fact that the example image and each of the stored images are indexed according to an image indexing method as briefly defined above.
By the use of such a method for indexing the example image and the images stored in the database, the image search method thus obtained makes it possible to obtain a search result which is much more precise than the search systems of the prior art which do not use this type of image indexing.
This is because on the one hand, for each image in the database, the database manager has taken care to specify the semantic content of the image by the definition of regions of interest in the image, these being taken into account through the vector W(Im) present in the index of the image. The user, on the other hand, through the data item of the second type associated with the example image, can also specify his request by choosing, in the image, certain regions which correspond to that which he wishes to find. Calculation of a vector W(Im) associated with the index of the image then makes it possible to take into account these regions of interest in the search.
The invention also concerns a device for seeking images, from an example image, from amongst a plurality of images stored in a database. In accordance with the invention this device has means adapted to implement a method of indexing and/or a method of seeking images, as succinctly defined above in connection with the second aspect of the invention.
The present invention also concerns a computer, having means adapted to implement a method of indexing and/or a method of seeking images, as defined above in relation to the second aspect of the invention, or having an above-mentioned device for seeking images. The invention also relates to a computer program containing one or more sequences of instructions able to implement such an image search method when the program is loaded and executed in a computer. The invention also relates to an information carrier, such as a diskette or compact disc (CD), characterised in that it contains such a computer program.
The advantages of this image search device, this computer, this computer program and this information carrier are identical to those of the image indexing/search methods as succinctly disclosed above.
Other particularities and advantages of the invention will also emerge from the following description.